This invention relates to temperature indicators, and more particularly to a pop-up type of temperature indicator commonly used for indicating the cooking temperature of poultry and other meats.
In the past, there have been a number of temperature indicators having a pop-up type plunger for indicating when a preselected cooking temperature has been reached. Such temperature indicators have been disclosed, for example, in U.S. Pat. Nos. 945,978; 3,090,235; 3,548,780; 3,682,130; 3,693,579; 3,713,416; 3,759,103; 3,811,402; and 3,965,849. These temperature indicators are customarily used for indicating when poultry or other meat has reached a desired internal temperature. The temperature indicator is typically placed in the poultry or meat prior to packaging and distribution.
In recent years, most of these temperature indicators have included a nylon housing with a pointed tip to facilitate pushing the temperature indicator into the poultry. A plunger inside the housing is normally held in a locked position by a quantity of solidified fusible material such as a fusible metal alloy. When the desired temperature is reached, the fusible alloy melts, releasing a coil spring inside the housing for pushing the plunger out of the housing to signal that the desired internal temperature has been reached.
The prior art temperature indicators suffer from a number of disadvantages. For example, in recent years the fusible metal alloy used in these temperature indicators has become relatively expensive, and for this reason there is a need to minimize the amount of the alloy used in such temperature indicators to reduce the added cost to the consumer as much as possible. For example, it is common for such fusible metal alloys to include indium which is a very expensive metal. In recent years, the cost of some fusible metal alloys containing indium has risen to as high as about $60-70 per pound.
In some prior art temperature indicators, when the fusible material melts, it shatters and metal particles can pass outside the housing of the temperature gauge and into contact with the food.
Of primary concern is the accuracy of pop-up type temperature indicators. The temperature indicators commonly used today have a nylon housing with a pointed tip for being inserted in the poultry. The temperature of the poultry is sensed by the housing and transferred to the fusible alloy. This can result in errors of about 3.degree. F., since the plastic materials commonly used with such temperature indicators are relatively poor heat conductors, and do not consistently sense temperatures uniformly.
The present invention provides a pop-up type temperature indicator which overcomes the above-mentioned disadvantages of prior art temperature indicators.